Milky Way's Local Arm Larger Than Previously Thought

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INDIANAPOLIS — Our home in the Milky Way could be much
larger than ever thought before, according to a new study.

Astronomers using the National Science Foundation's Very Long
Baseline Array (VLBA) found that the area of the galaxy that
holds Earth and the rest of the solar system is a prominent
feature of the spiral galaxy.

The solar system exists in a part of the galaxy known as the
Local Arm. Until now, scientists thought that this particular
part of the Milky Way
was just a tiny spur between two large branches known as the
Sagittarius and Perseus arms.

"Our new evidence suggests that the Local Arm should appear as a
prominent feature of the Milky Way," Alberto Sanna, of the
Max-Planck Institute for Radio Astronomy said in a statement.
Sanna presented these findings at a news conference during the
222nd meeting of the American Astronomical Society.

In fact, the Local Arm looks to be as long as 16,000 light-years
wide, Sanna said.

Scientists can't be sure what the Milky Way galaxy truly looks
like from the outside, because we are stuck within it.
Researchers have to measure distances between objects in the
Milky Way to understand exactly where something might fit within
the context of the rest of the cosmic neighborhood.

"Based on both the distances and the space motions we measured,
our Local Arm is not a spur," Sanna said."It is a major
structure, maybe a branch of the Perseus Arm, or possibly an
independent arm segment."

The new research, which uses data collected between 2008 and
2012, used simple trigonometry to understand the placement of the
solar system in relation to the rest of the galaxy.

"By observing objects when Earth is on opposite sides of its
orbit around the sun, astronomers can measure the subtle shift in
the object's apparent position in the sky, compared to the
background of more-distant objects," National Radio Astronomy
Observatory officials wrote in a statement. "This effect is
called parallax, and can be demonstrated by holding your finger
close to your nose and alternately closing each eye."

Scientists used parallax to measure the distances to star-forming
regions of the Milky Way, because methanol and water molecules
there boost radio waves (like those used by the VLBA), making it
easier for researchers to collect accurate data.